A proxy payment card (hereinafter simply “proxy card”) is a physical card, similar in appearance to a traditional magnetic stripe payment card (e.g., a credit card, debit card or pre-paid card) and readable by a traditional magnetic card reader, but it can emulate one or more other payment cards. For example, a proxy card of a particular cardholder may be configurable to emulate either the cardholder's Visa card or MasterCard for any purchase from any given merchant, according to the cardholder's choice at the time of purchase. A proxy card may include electronics, an emulator coil, and other components to store multiple sets of magnetic stripe data, for example, card data for two or more payment cards, and can emulate any one of the sets of stored magnetic stripe data. When such a proxy card is swiped through a magnetic read head of a magnetic stripe card reader, a microcontroller on the proxy card “plays back” a set of magnetic stripe data sequentially to an emulator coil on the proxy card. The play back causes the emulator coil to produce a magnetic field. The changing magnetic field induces a read signal in the magnetic read head coil. The read signal is then decoded by the magnetic read head to obtain the magnetic stripe data.
The above described play back method to emulate magnetic stripe data depends on the speed at which a proxy card is swiped and can lead to decoding error. For example, if a user swipes a proxy card at a swipe speed faster than the rate of play back, the magnetic card reader may not be able to obtain a full read signal. Consequently, the user may have to swipe the proxy card more than once before the magnetic read head can obtain a successful read. That wastes both the cardholder's and the merchant's time and causes annoyance to both of them.